Implementing Safe and Effective Biological Controls

    We have repeatedly asked vector control and public health officials why they don't implement some very safe and highly effective biological controls.  In a meeting with Sacramento City Councilmember Rob Fong on July 27, 2007, Dave Brown said that they did not use a mosquito-parasitic nematode, Romanomermis culicivorax, and a fungus, Lagenidium giganteum, because 1) they are not commercially available, 2) Romanomermis does not work with Culex mosquitoes, and 3) the agents are not cost effective.  We know that they are not commercially available, and this is because they must be cultured on mosquitoes, or in vivo, which is somewhat labor intensive.  But, both the Sac-Yolo and Sutter-Yuba districts used to culture R culicivorax in vivo in the late 1970's and early 1980's.  After the meeting we sent him an email that contained the following two requests:

•  Please supply any detailed financial analyses you have that you believe demonstrate that the local culturing of these two agents, by your agency for example, would not be cost effective (after all, you already grow mosquito fish).

•  What exactly do you mean by your statement that Romanomermis "does not work" with Culex mosquitoes, what is your evidence, and what are your reasons and evidence for not culturing and using Lagenidium?

    His email response to the first question via an email dated August 2 was:

"You are correct that both the Sutter-Yuba MVCD and the Sacramento-Yolo MVCD cultured Romanomermis culicivorax in the late 1980's and early 90's ... both Districts stopped doing this because it was extremely labor intensive, required controlled space, failures would occur during the process and there were already effective and efficient larvicides available. (Bacillus thuringiensis var. israelensis and methorprene, to name two.)

Of note, a researcher at UC Riverside is working with a researcher in Mexico to develop a process to mass produce R. culicivorax. We continue to watch this with interest and will monitor progress.

You continue to miss the point of larviciding and adulticiding. While we welcome more larvicides, none of them will be effective unless we know where the larval habitats are.  Back yard sources continue to be a major problem for us and educating the public is key to eliminating these sites and changing public behavior regarding water use."

The main thing to note is that no financial analyses whatsoever are supplied -- Brown just makes some general assertions that do not demonstrate that these agents are not cost effective.  It seems to us that no statements about cost effectiveness can be taken seriously unless they contain detailed financial analyses of such things as cost of labor, materials, and facilities, as well as comparisons with the millions of dollars the District is spending on aerial adulticiding and careful comparisons of the efficacy of the different approaches. 

    There are also errors in his statement. For example, cultures of R culicivorax were initiated in the late 1970's and not the 1980's.  Furthermore, he notes the Riverside work, as if these were new developments.  What is new there is a study that shows a much higher infectivity into Aedes egyptii, the Yellow Fever vector, than the 30% we know of for Culex pipiens.  And, in a recent communication to us Dr. Platzer at Riverside had indicated in his letter that Dr. Pacheco-Perez in Mexico had improved the cost effectiveness of culture systems.  Moreover, we do not miss the point about larvaciding and adulticiding.  The main point is that scientific research shows that if adulticiding is done as late in the season as is done by the District, there is no chance that they can get the kill rates they need to slow the transmission of WNv to humans.  What they need to do, among other things, is to use these very effective biological controls, and possibly others, early in the season.  These two can last over several seasons if done properly, and this insures that mosquito larvae begin to be killed at the very beginning of the season.  But again, no cost figures were given for the various components of an operation to culture these two biological controls, and the claim that they are not cost effective remains an unsupported assertion.

    His email response to the second question via the same email note was:

"Lagenidium giganteum is a water mold that requires specific water parameters to be effective.  Many of our culex species come from very 'foul' sites.... for example, the 50,000+ catch basins in Sacramento are not suitable sites to use L. giganteum.  Yet these sites are a major producer of culex pipiens, which has been clearly identified as an efficient vector of West Nile virus.

Our goal is not to always treat sites with pesticides; rather, it is to implement Best Management Practices so we can eliminate pesticide use all together. We notified the City of Sacramento over four years ago of the potential problem that existed in that area. We were told that it would be too expensive to make these changes to the system. Therefore, the district  currently uses Bacillus sphaericus and methoprene in these sites because of their tolerance to foul water areas and their ability to control mosquitoes for an extended period of time (in some cases, more than 90 days). However, their effectiveness can be compromised due to changes in water flow, increases in organic loads, etc... that can result in emergence of adult mosquitoes.

As Dr. Kramer stated, the Department of Health Services supported and funded the registration of L. giganteum for several years while a private company located in Davis (AgraQuest) attempted to culture and produce it. They were unable to do so reliably. Our district also supported AgraQuest financially and through field trials, and will continue to support the development of new and effective larvicides that present themselves as viable alternatives or options.

However, the fact still remains that no larvicide exists that will control mosquitoes if it is not applied to where they are. An abandoned or unmaintained backyard swimming pool, bucket of water, catch basin that has been flushed out, water trough, etccc...are all capable of producing literally thousands of adult mosquitoes if they have not been treated effectively."

The first thing to note about this response is that no scientific evidence is supplied, just assertions, and we had explicitly asked for evidence.  Also, how is 25,000 square meters of bypass a moving target that would disrupt these agents?  We have the same question about the ponds and the arboretum around Davis.  As far as we know the AgraQuest effort was an attempt at an artificial culture, we are aware that such cultures do not produce the same infectivity or viability of the natural culture, and this is why we specifically asked about culturing "by your agency."

    Dave Brown continues to assert that the back yards are the biggest problems in terms of breeding sites, but no data is ever supplied, and we have heard of no attempts to measure this, including possible random surveys.  Quick "control" of adult population isn't real reduction of the numbers, because we get .2N new recruits into the stage each day.  Newton and Reiter1 indicate that populations rebound within 3-11 days if no additional larval control is applied at the same time.  But again, Brown's answer consists entirely of assertions and does not supply evidence or detailed analyses as to why the agents supposedly don't work.

    Because Brown supplied no evidence of formal analysis of these questions, we filed a Public Records Act request on August 7, 2007, for any documents relating to these issues, explicitly asking about in vivo culturing of the agents.  However, this produced nothing other than the email note from Brown we had already received, from which we quote above.  So, we have asked for the documentation to support fiscal analysis, and they have indicated that they have no documentation.  They have also indicated that they have no documents to support their assertion that production and use of these two safe and effective biological agents does not work.  It would thus seem clear that the District's failure to culture and use these two safe and effective biological agents does not depend on a careful and thorough analysis of the main issues but depends on hunches and vague assertions.  We believe that the citizens of these two counties deserve much better.
1.  Elizabeth A. C. Newton and Paul Reiter, "A Model of the Transmission of Dengue Fever with an Evaluation of the Impact of Ultra-Low Volume (ULV) Insecticide Applications on Dengue Epidemics," Am. J. Trop. Med. Hyg., 47(6), 1992, pp. 709-720.